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Global climatic and palaeogeographical changes generated a siliciclastic–carbonate system with high organic matter accumulations in a shallow sea during the lower Permian in Western Gondwana. The 60 m thick mixed siliciclastic–carbonate succession (Irati Formation and the base of the Serra Alta Formation) from the Paraná Basin represents a singular record of the interplay between carbonate production and siliciclastic input, providing a window of opportunity to integrate large‐scale depositional architecture with facies and geochemical analyses. The detailed study of cores supported by outcrop columnar sections revealed a siliciclastic‐dominated, retrogradational to aggradational facies, and a carbonate‐dominated, mixed aggradational to progradational facies composing three depositional sequences that record an outer‐ramp and mid to upper‐ramp. An integrated approach based on the description of facies and microfacies, organic geochemistry and mineralogical composition, indicated high‐frequency palaeoenvironmental changes during the evolution of this restricted basin. Climate changes, resulting in humid and dry phases, produced ideal conditions for high organic matter production and dolomite formation. The high organic matter production (humid phases) in addition to the restricted condition was responsible for the anoxic bottom waters that were widespread due to the low angle and homoclinal platform. Nutrient‐rich freshwater inflows in the anoxic and hypersaline restricted basin created a density‐stratified water column causing low‐salinity surface and anoxic bottom water, which allowed planktonic life, typical of lakes, such Botryococcus braunii, to flourish in the photic zone and sulphur bacteria to populate below the chemocline. Microbial activity induced primary dolomite precipitation (dry phases) and widespread formation of synsedimentary dolostone. Freshwater inflow and marine incursions are reflected in the organic matter accumulation (kerogen types I and II, respectively), generating bituminous shale with high total organic carbon (5 to 27 wt.%). [ABSTRACT FROM AUTHOR]

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Sinusichnus Gibert 1996 is recorded for the first time in the Oligocene-Miocene Pirabas Formation of Northern Brazil. In these Oligocene-Miocene carbonate deposits, Sinusichnus sinuosus is characterized by horizontal, highly regular sinusoidal burrow systems with T- and H-shaped branching points. The main difference between the S. sinuosus described herein and other occurrences worldwide is the anomalous diameter of the burrows (4 to 10 cm). These trace fossils occur in organic matter-rich, wackestone/packstone and laminated mudstones interbedded with boundstones deposited in an inner carbonate platform paleoenvironment. The exceptional size of the studied S. sinuosus could have been associated to the producer's size, which may be attributed to construction by large crustaceans, similar to fossils found within the Pirabas Formation. Also, the sinusoidal morphology and retrusive spreiten could be a result of the fodinichnial/domichnial behavior. [ABSTRACT FROM AUTHOR]

Organic matter from the cap dolostones overlying the Marinoan-age glacigenic diamictites of the Araras Group, Amazon craton, has been studied to reconstruct the post-glacial ecosystem. Molecular fossils indicate that the post-Marinoan ecosystem was marked by an apparent decline in marine algal diversity. The proliferation of red algae may be explained by environmental changes, such as a massive nutrient input accompanying continental weathering after the ice thaw and a dimer light penetrating sea water due to the drowning of the platform. In addition, the presence of green sulphur bacteria indicates that sea water was stratified with an anoxic (possibly euxinic, i.e. sulphidic) layer at the water–sediment interface. Sulphur cycling probably occurred at the redox boundary as suggested by the recognition of active sulphate reduction. This observation supports a microbially induced model for the formation of the cap dolostones. [ABSTRACT FROM AUTHOR]